Preparation of alkali metal carbonates from the corresponding sulfates or sulfides



United States Patent 3,401,010 PREPARATIUN 0F ALKALI METAL CARBONATES FROM THE CORRESTONDING SULFATES 0R SULFIDES Salvatore Guerrieri, Rowayton, Conn, assignor to The Lummns Company, New York, N.Y., a corporation of Delaware Filed Sept. 17, 1964, Ser. No. 397,340 9 Claims. (CI. 23-63) ABSTRACT OF THE DHSCLOSURE A process and apparatus for producing alkali metal carbonates by countercurrently contacting the corresponding sulfates and sulfides with a reaction 'gas containing either hydrogen and carbon monoxide or water and carbon dioxide, respectively, the contacting being effected at a temperature above 1200 F. and below the softening point of the carbonate. The apparatus comprises a plurality of perforated trays arranged in a tortuous path in an upper portion of a vessel, a combustion chamber for producing the reaction gas, heat transfer surfaces for regulating the temperature of the combustion gas in the lower portion of the vessel and a perforated plate to reduce radiation to the perforated trays.

This invention is concerned with a process for forming metal carbonates and, more particularly, relates to conversion of metal sulfates and sulfides to the corresponding metal carbonates.

Sulfates and sulfides of metals either as they occur in nature or as they are derived as a by-product of a chemical process often have little or no commercial value whereas the corresponding carbonates do. For example, relatively large deposits are known of potassium sulfate. The sulfate has low commercial value but the potassium carbonate has a large and expanding market. Another example is the smelt withdrawn from the recovery furnaces of a pulp mill. The smelt is essentially a mixture of sodium carbonate and sodium sulfide. In the practice of sulfite cooking, it is necessary to convert sodium sulfide to the carbonate first, and then to the sulfite. Present processes for accomplishing this conversion are complex and expensive and are, therefore, used only to a limited extent. It is well recognized that sodium sulfite pulping would be more widely adopted if a relatively simple, inexpensive recovery process were available. The present invention is directed to a less expensive and simple way to effect conversions of such sulfates and sulfides to their corresponding carbonates.

It is an object of the present invention, therefore, to provide a process for converting metal sulfates and metal sulfides to their corresponding metal carbonates. Another object is to provide a conversion system comprising interrelated reaction, heat exchange and combustion zones for effecting the desired conversions. A particular object is to provide a process for readily converting potassium sulfate to potassium carbon-ate. Another particular object is to provide a process for efficiently converting sodium sulfide, especially in the form of a sodium sulfide-sodium carbonate smelt, to sodium carbonate. Other objects of the invention will be apparent from the following description.

The invention is now described with reference to the accompanying drawings. FIGURE 1 is an elevational view in section of a preferred embodiment of a contactor or reactor. FIGURE 2 is a schematic flow diagram illustrating a preferred embodiment for forming potassium carbonate. It will be recognized that the drawings are highly diagrammatic in form.

Finely divided potassium sulfate is charged through line 1 to an upper portion of contactor or reactor 2 and is deposited upon tray 3 of reaction zone 4. Tray 3 is continuous adjacent reactor wall 5 and is perforated for the remainder thereof, and terminates with extension 6. Fine particles of the sulfate flow across tray 3 and downwardly through passageway 7 to the next successive and similar tray 8, which terminates with extension 9, and passageway 10. In sequence, particles flow downwardly through reaction zone 4 to tray 11 having extension 12 and passageway 13, and to tray 14 having extension 15 and exit passageway 16. Carbonate particles formed, as described below, in reaction zone 4 are withdrawn through line 17 with connects with exit passageway 16.

In reaction zone 4, downwardly flowing particles of potassium sulfate are in contact at elevated temperature with combustion gases containing carbon monoxide and hydrogen with the result that the sulfate is converted to the corresponding potassium carbonate. Among the reactions which may take place in reaction zone 4, (3) and (4) of the following are the most probable:

Reactant gas is formed in combustion zone 18 by burning therein a fuel, such as a fuel oil, and air charged, respectively, through lines 19 and 20. Reactant gases pass upwardly from combustion zone 18 to heat exchange zone 21. In the latter, some heat of combustion can be recovered via heat exchange surfaces 22 to reduce the temperature of the reactant gases to a. temperature desired for the reaction zone 4. Perforated baffle 23 is shown in heat exchange zone 21 as reducing radiation to tray 14 from heat exchange zone 21 and thus reduce the possibility of excessive temperatures on tray 14 or of hot spots. The

temperature of the reactant gases in the heat exchange zone 21 can also be suitably adjusted by introducing a coolant in fluid form, such as steam, to zone 21 through line 24 and spray nozzle 25.

Efliuent gases are removed from reactor 2 through line 26, after passing through a cyclone separator (not shown) or equivalent device to remove from the effluent gas, and to return to the reactor, any solids entrained by the efi luent gas. The effluent gas formed in the conversion of potassium sulfate to potassium carbonate contains hydrogen sulfide which can be recovered by known techniques (not shown) for use as such, or can be converted to elemental sulfur or useful sulfur-containing compounds. In the practice of this invention, temperature control is a salient feature. In reaction zone 4, the temperature is maintained above about 1200 F. and below the softening point of the downwardly flowing solids therein (e.g. K CO Temperature control is achieved by proper adjustment 0f the temperature of the upwardly flowing combusion gases as they flow through heat exchange zone 21 to reaction zone 4. Preferred temperatures for the latter zone (4) for the conversion of potassium sulfate to the carbonate, are from about 1200 F. to about 1550 F.

Another feature cooperating to provide the effective conversions of this invention is control of reactant gases. Total or partial combusion of fuel in. combustion zone 18 can be achieved by selection of suitable fuels and by proportioning of fuel, air or oxygen, and other combustion variables. For example, for the conversion of potassium sulfate to the corresponding carbonate, reactant gases containing relatively high concentrations of carbon monoxide and hydrogen are used. Whereas, for the conversion of sodium sulfide per se, or in the form of a sodium sulfide-sodium carbonate smelt from a pulp mill recovery furnace, reactant gases rich in carbon dioxide and water vapor are desired. In the latter instance, sodium sulfide reacts in accordance with the following equation:

Conversion of the sodium sulfide is preferably effected in reaction zone 4 at a temperature from about 1200 F. to about 1500 F.

As indicated above, air or oxygen or mixtures of the same can be used in the combustion zone 18, although air is preferred in view of its much lower cost. The dilution effect of nitrogen upon the desired combustion gases including carbon monoxide, carbon dioxide, hydrogen and Water vapor, is small and in no sense disadvantageous.

Fuels used in the production of reactant gases can be hydrocarbon ranging from methane to Number 6 fuel oil, or may be solid fuel such as coal or coke.

Pressures maintained in reaction zone 4 range from about 10 pounds per square inch absolute (p.s.i.a.) to about p.s.i.a.

It will be understood that reaction zone 4 can comprise a zone through which fine particles of potassium sulfate pass or shower downwardly to meet a counter-current flow of reactant gases, or can comprise, as shown by the preferred embodiment in FIGURE 1, a plurality of fluidized beds providing countercurrent and intimate contact of solids and gases. Broadly, then, at least one contact of solids and gases is provided in reactant zone 4.

Metal sulfates and sulfides have been illustrated above by potassium sulfate and sodium sulfide. However, all alkali metal sulfates and sulfides are contemplated herein, as are generally all metal sulfates and sulfides.

The present invention is more fully described and illustrated with reference to FIGURE 2, in the following example. It is to be understood, however, that the inven tion is not to be limited to any specific form of materials or conditions set forth in the example, but is limited solely by the description in the specification and the appended claims.

One mole of finely divided potassium sulfate at 100 F. is introduced through line 30 into the upper portion of a reactor 31. The finely divided potassium sulfate is passed in a countercurrent flow to reactant gases introduced through line 32 and distributor 33 into reactor 31. The reactant gases are formed by introducing 1.25 moles of a hydrocarbon fuel at 100 F. in line 34 and air containing 1.25 moles of oxygen at 100 F. in line 35, into a gas generator 36. The reactant gases comprised of 2.5 moles of carbon monoxide, 2.5 moles of hydrogen, and 4.7 moles of nitrogen, and are withdrawn from gas generator 36 and passed to reactor 31 through line 32. Additional fuel, if desired, can be added to the reactant gases in line 32 through line 37. The gas generator 36 can also serve as a waste heat boiler by passing boiler feed water through line 38; in this way, some of the heat of combustion is recovered and the temperature of the reactant gases is controlled.

Reactant gases in line 32 enter reactor 31 at about 1340 F. As reaction occurs between the potassium sulfate and the gases, the temperature in the reactor is increased to about 1500 F, and potassium carbonate is formed. The carbonate is removed from reactor 31 through line 40, is passed through cooler 41, and is removed from the process through line 42. Approximately one mole of potassium carbonate is so obtained.

Effluent gases and solids entrained therein, at about 1500 F., are removed from reactor 31 through line 43 and are passed into a cyclone separator 44. Solids are separated from the effluent gases and are returned through line 45 to reactor 31. Efiluent gases (8.7 moles) containing hydrogen sulfide, are removed from cyclone separator 44 through line 46. Such gases can be removed from the system through line 46a for recoveryof H S or sulfur, etc. (not shown). Preferably, the efiluent gases are passed through line to line 47 to be introduced into boiler 48. Air containing two molar proportions of oxygen, at F., is also charged to boiler 48 via line 49. In boiler 48, hydrogen sulfide is converted to sulfur dioxide. Combustion products formed in 48 are vented to the atmosphere through line 50 at a temperature of 600 F or can be passed to recovery means (not shown) for separating sulfur dioxide. Water in line 39 is passed through boiler 48, and heated to a temperature to form steam which is removed through line 51. Approximately 20 moles of boiler feed water are introduced through line 38, and a similar quantity of steam is recovered in line 51.

Pressure throughout the system is substantially atmospheric.

For the conversion of sodium sulfide to sodium carbonate in the system described directly above, reaction conditions can be modified. One mole of sodium sulfide is introduced in line 30 and approximately one mole of sodium carbonate is withdrawn through line 42. Reactant gases are formed in generator 36 from 0.5 mole of fuel in line 34, and air containing 1.5 moles of oxygen in line 35. The reactant gases are comprised of 1.0 mole of carbon dioxide, 1.0 mole of water vapor, and 5.6 moles of nitrogen. The reaction temperature in reactor 31 is maintained at about 1400* F. About 6.6 moles of efiluent gases in line 46 can be withdrawn from the system through line 46a. 9.0 moles of boiler feed water can be passed through boiler 36, and a corresponding quantity of steam removed through line 39.

While the invention has been described in detail according to preferred materials and preferred operating conditions, it will be obvious to this skilled in the art that changes and modifications can be made, without departing from the spirit or scope of the invention, and it is intended in the appended claims to cover such changes and modifications.

I claim:

1. A process for producing an alkali metal carbonate comprising:

(a) passing a finely divided solid alkali metal sulfate in countercurrent contact in a reaction zone with a reactant gas at a temperature above 1200 F. and below the softening point of the corresponding alkali metal carbonate, said reactant gas being a gas containing hydrogen and carbon monoxide, said contacting converting the compound to the corresponding alkali metal carbonate; and

(-b) recovering the alkali metal carbonate.

2. The process defined by claim 1 wherein the alkali metal compound is potassium sulfate and the alkali metal carbonate is potassium carbonate.

'3. The process defined by claim 1 wherein the pressure in said reaction zone varies from about 10 to about 30 pounds per square inch absolute.

4. A process for producing an alkali metal carbonate comprising:

(a) passing a finely divided solid alkali metal sulfate through a reaction zone of a reactor, said reactor containing in addition to the reaction zone, a combustion zone and heat exchange zone;

(-b) reacting a free-oxygen containing gas and a hydrocarbon in the combustion zone to produce a reaction gas, containing carbon monoxide and hydrogen;

(c) passing said reaction gas through the heat exchange zone wherein the temperature of the gas is adjusted to a temperature sufiicient to maintain the temperature in the reaction zone at a temperature above 1200 F. and below the softening point of the alkali metal carbonate;

(d) passing the reaction gas through the reaction zone in countercurrent contact with the alkali metal sulfate, the contacting being effected at a temperature 5 above 1200" F. and below the softening point of the corresponding alkali metal carbonate whereby said alkali metal sulfate is converted to said alkali metal carbonate; and

(e) recovering the alkali carbonate from the reaction zone.

5. The process defined by claim 4 and further comprising: recovering hydrogen sulfide from said reaction zone and reacting said hydrogen sulfide with an oxygen containing gas to produce sulfur dioxide.

6. The process defined by claim 4 wherein the alkali metal sulfate is potassium sulfate and the contacting is effected at about 150 0 F. to produce potassium carbonate.

7. The process defined by claim 4 wherein a coolant is introduced into said heat exchange zone.

8. The process defined by claim 4 wherein steam is introduced into said heat exchange zone.

9. The process defined by claim 4 wherein said solid is cascaded downwardly as a fluid bed through a plurality of trays comprising said reaction zone.

References Cited UNITED STATES PATENTS 2,529,366 11/1950 Bauer. 2,716,587 8/1955 Hillard 231 2,732,283 1/1956 Clukey 23-48 X 2,750,258 6/1956 Jukkola et a1. 231 X 3,133,789 5/1964 Guerrieri 23-63 X 3,236,589 2/1966 Reinhall ct a1. 2348 2,233,155 2/1941 Adams. 3,322,492 5/1967 Flood 23-48 X FOREIGN PATENTS 1,786 1873 Great Britain.

OTHER REFERENCES Handbook of Chemistry and Physics, 36th Ed., Chemical Rubber Publishing Co., 1955, pp. 486, 487, 532, 533, 546 and 547.

20 OSCAR R. VERTIZ, Primary Examiner.

G. T. OZAKI, Assistant Examiner. 

